This invention belongs to the manufacturing fields, specially relates to the structure design of a type of multi-function parallel machine tool driven by sliders and an extensible strut.
The movement mode of the traditional machine tools is that the cutter and workpiece move along fixed guide ways. However, this mode has inherent limitations. For example, in order to maintain high stiffness and therefore high machining precision, traditional machine tools need bulky machine body, firm column and steadfast guide way systems, which increase weight, manufacturinpg cost and transporting difficulty. Moreover, that the cutter can only feed along, the guide way limits its machining dexterity.
To meet the increasing demand of parts with complex and special shapes, the machine industry adopts all kinds of possible strategies. For instance, more bulky structure and expensive fixtures are used to get stronger machining capability. Such strategies usually result in longer manufacturing period and cost. Furthermore, the machining quality may not be very reliable. Over the years, a new type of parallel machine tools (PMT) has occurred, of which extensible struts substitute traditional fixed guide way systems, and, frame structure substitute heavy machine body, pillar and other components.
The numerical control system of a traditional machine tool is based on Cartesian coordinate, and each guide way system corresponds to one degree of freedom. However, the numerical control system for PMT is based on the controlled axis of PMT, that is, the struts. The lengths of extensible struts or positions of sliders determine the position and orientation of cutter. Therefore PMT can realize the machining task by adjusting the lengths of extensible struts or the positions of sliders. As a new type of manufacturing equipment, PMT changes the mode of relative motion between the cutter and the workpiece, and increases the cutter""s movement dexterity. These advantages enable PMT to have more powerful machining ability and higher controlling dexterity.
The representative structures of PMT can be mainly classified into two types. One is the extensible strut type PMT, in which the frame is used as supporting structure. One end of the extensible strut is connected with the node on either top or bottom of the frame, and the other end is connected with the moving platform on which the cutter is fixed. Because of frame-supporting structure, this type of PMT has higher stiffness than traditional machine tools when they have the same machining capability. However, the motions of the extensible struts are coupling, and their lengths vary with the time. Therefore it is difficult to calibrate the thermal effect. Moreover, the structure comprises many special parts which don""t have high standardization level.
The other type is the slider type PMT, in which the frame is also used as supporting structure, but the length of each strut is steady. One end of the strut is connected with the slider moving on a guide way, and the other end is connected with the movable platform. This type of machine tool has not only the advantages of the first type of PMT, but also other beneficial performances. For example, the steady length struts can effectively reduce the error caused by the thermal effect. Another distinct characteristic is the motion of the movable platform along guide way is not coupling with the motion in other directions, which fits to machining long shape parts with complex surfaces. The deficiency of this type of PMT is that the machining dexterity of the cutter in other directions is correspondingly lower than that along guide way. Therefore, although it has the superiority to machining long pats, its capability of machining other type of parts is weaker than that of the first type of machine tool.
By overcoming the shortages of the two types of PMT mentioned above and synthesizing their merits, this invention designs a new machine tool structure with multi-purpose, including cutting, milling, assembling, fluid work machining and measuring. Compared with traditional machine tools, this invention possesses several advantages as simpler structure, better cutter dexterity, faster cutter feed rate, higher accuracy, and better thermal effect calibration. The invention can sufficiently meet the user""s demand for three to five axes machine tools.
The invention designs one type of parallel machine tool structure driven by the slider and extensible strut. It includes:
Two vertical (or one horizontal) guide ways, two active sliders mounted on guide ways, two linear drive units used to move the active sliders, two struts, one movable platform to assemble cutter, one workbench to fix workpiece, one slave slider and one controlled extensible strut.
The main feature of this invention is:
The ends of two struts are hinged together, and the other two ends of them are hinged with the two active sliders respectively. The salve slider is linked with one active slider and moves on the vertical guide way. One end of the controlled extensible strut is hinged with the salve slider, and the other end of it is hinged with the movable platform. The movable platform is hinged with two struts by revolute joints. All the components mentioned above constitute parallel loop chains with three degree-of-freedom. The worktable is independent of the parallel loop chain.
The slave slider can be assembled on different positions on the guide way, and the position of the hinge joining the controlled extensible strut with slave slider can also deviate a desired distance from the guide way. Therefore, the machine tool is able to adapt to different machining situations.
The platform may be added a rotate function. The workbench is composed of the slide table, servomotor, guide way as well as worktable with rotate and move function.
The controlled extensible strut comprises a hollow cylinder with one cover, a servomotor, a hollow linear guide bar, a ball screw and ball a female screw driven by servomotor, a connector connecting the ball female screw and linear guide bar. The hollow cylinder with one cover is assembled with the servomotor, linear guide bar, connector, ball screw and ball female screw one by one.